1. Field of the Invention
The present invention relates to an ultrasound imaging apparatus that generates image data for supporting treatment and examination using a puncture needle, and also relates to a method for generating an ultrasound image.
2. Description of the Related Art
The mortality rate for cancer, which is one of the three major diseases, has been increasing yearly, and early diagnosis and treatment of cancer is strongly desired. For example, liver cancer accounts for approximately 10% of all cancers, and the percentage has been increasing. On the other hand, advancement of the technology of medical image diagnosis apparatuses such as an ultrasound imaging apparatus, an MRI apparatus and an X-ray CT system is remarkable, and medical image diagnosis apparatuses has been essential for early detection of various cancers including liver cancer mentioned above.
To be specific, three-dimensional imaging by an X-ray CT system, which is combination of high-speed rotation helical scan with a multi-detector of, e.g., 64 rows, has been in practical use. Moreover, owing to increase in performance of gradient magnetic field systems, high-frequency magnetic field systems and RF coil systems, three-dimensional imaging by an MRI apparatus capable of high-speed imaging has been in practical use.
Observation of volume rendering image data, etc., obtained by these three-dimensional imaging methods has significantly increased the diagnostic ability as compared with a conventional two-dimensional imaging method.
On the other hand, an ultrasound imaging apparatus allows real-time observation using two-dimensional image data by a simple operation of making an ultrasound probe in contact with a body surface. Besides, a method of acquiring three-dimensional B-mode image data and color Doppler image data in real time by using an ultrasound probe in which transducers are one-dimensionally arranged and mechanically oscillating the transducers has been developed. Moreover, another method of acquiring three-dimensional B-mode image data and color Doppler image data in real time by using a so-called 2D array probe in which transducers are two-dimensionally arranged has been developed.
As a method for treating liver cancer mentioned above, (a) anticancer agent injection into the liver artery, (b) transcatheter arterial embolization (TAE), (c) minimally invasive therapy, (d) laparotomy, etc., are common. In recent years, the minimally invasive therapy with a simple procedure and less burden on a patient is particularly remarkable. The minimally invasive therapy includes the PEIT (Percutaneous Ethanol Injection Technique) and microwave ablation. A puncture needle used in these therapies is inserted into a patient with observation of an image displayed in real time.
Further, in recent years, RFA (Radio Frequency Ablation) has been attracting attention as one of the ablation therapies, and clinical application thereof has already begun. In this RFA, Cool Tip, which is a single needle, or RITA, which is an expandable needle, is used as the puncture needle. The puncture needle is usually inserted into a tumor percutaneously from the body surface with observation of an image, but may be inserted with observation of the surface of the liver by a laparoscope. Moreover, the puncture needle may be inserted with observation of an ultrasound image acquired by a special small ultrasound probe placed on the surface of the liver.
By performing the abovementioned puncture therapy with observation of two-dimensional image data acquired in real time by an ultrasound imaging apparatus, the efficiency of the therapy and the safety of the therapy have been drastically increased. Besides, in recent years, various puncture therapies performed with observation of a three-dimensional image have been proposed (e.g., Japanese Unexamined Patent Application Publication No. 2007-125169 and Japanese Unexamined Patent Application Publication No. 2007-215672).
With the method according to the conventional art of performing the puncture therapy with observation of three-dimensional image data acquired in real time by an ultrasound imaging apparatus, it is possible to three-dimensionally grasp the insertion direction of a puncture needle, the position of the tip, or the like. Therefore, it is possible to further increase the accuracy of insertion of a puncture needle into a treatment target site as compared with the puncture therapy performed with observation of two-dimensional image data.
However, it is difficult to acquire three-dimensional image data representing a wide range that satisfies both high spatial resolution and high temporal resolution (real-time property). Therefore, with the method according to the conventional art described above, in the case of acquiring image data representing a relatively wide treatment target site including liver cancer or the like, and image data representing a puncture needle inserted into this treatment target site and an area surrounding the puncture needle, it is difficult to simultaneously acquire image data representing a treatment target site that requires high spatial resolution and image data representing a puncture needle and an area around the puncture needle that requires high temporal resolution and high spatial resolution in order to track the tip of the puncture needle.